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New to car motor boats and need help


So I have a aircraft boat. But building a more family friendly boat going to be a 350 but don’t know what box to go with a stinger 2 to 1 or a 3.67 belt box 78” 3 blade h Series help please..
The first thing you need be aware of is that belt drive reductions (like direct drive applications) use LEFT hand propellers.
If you use a gear drive reduction, then you will be needing to use a RIGHT hand propeller.

H blades by nature of design like to spin fast (around 3K RPM) to be the most productive, as they were designed for direct drive applications. I don't remember seeing right hand H blades, although that admittedly means between little and nothing.

If they DID make such a critter, your proposed 2.09:1 gear ratio would be workable as turning a small block 6250 rpms is not outside the realm of possibility. However, to spin H blades 3k rpm with a 3.67 ratio would require 11,000 engine rpms, and be well outside the realm of 'family friendly' even if your masochistic streak and your wallet were that big.

Now with all that having been said, if the H blades are what's on your current A/C boat and you are going to reuse them, you will be needing a belt drive (not gear), but far less ratio than the 3.67 to do so. A 2:1 would be the first typical option; a 2.3:1 could work IF you perceive 6,900 engine rpm as 'family friendly'.
I kind of have the same question as you Yotaup. I'm new to the ownership side of airboats as a whole. I have a 12' Diamondback aluminum hull with a 350 DD and a 2 blade water walker prop. I'm looking to add a gearbox and change out the prop to maybe a 3 blade right hand prop. I will most likely go with an Ox, but my main concern is what ratio? I know a 350 crate motor can only do so much, but I have people telling me a gearbox will still make a world of difference.